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My February birthday fund-raising campaign for this website, Behind the Black, is now over. Despite a relatively weak initial three weeks, the last week was spectacular, making this campaign the second best ever.

 

Thanks to every person who donated or subscribed. It continues to astonish me that people who can read my work for free like it enough to donate money voluntarily. Words cannot express my appreciation for that support, especially in these uncertain times.

 

If you have been a regular reader and a fan of my work and have not yet donated or subscribed, please consider doing so. I take no ads, I keep the website clean from pop-ups and annoying demands (most of the time). Thus, I depend entirely on my readers to support me. Though this means I am sacrificing some income, it also means that I remain entirely independent from outside pressure. By depending solely on donations and subscriptions from my readers, no one can threaten me with censorship. You don't like what I write, you can simply go elsewhere.

 

You can support me either by giving a one-time contribution or a regular subscription. There are five ways of doing so:

 

1. Zelle: This is the only internet method that charges no fees. All you have to do is use the Zelle link at your internet bank and give my name and email address (zimmerman at nasw dot org). What you donate is what I get.

 

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Mars’ seasonally vanishing carbon dioxide polar cap

Buzzell dunes, March 19, 2019
Click for full image.

Since the onset of the Martian spring in the northern hemisphere back in March of this year, scientists have been busy using the high resolution camera on Mars Reconnaissance Orbiter (MRO) to monitor the expected sublimation and disappearance of the cap of dry ice that falls as snow to become a winter layer mantling both the more permanent icecap of water 7,000 feet deep as well as the giant dune sand seas that surround that northern icecap.

The image on the right was first posted here on Behind the Black on June 6, 2019 as part of a long article describing that northern polar icecap and its annual evolution. It shows a set of dunes that Candice Hansen of the Planetary Science Institute in Arizona, who requested the image, has dubbed “Buzzell.” When that picture was taken in March, the frozen dry ice layer of translucent carbon dioxide still coated the dunes. The image’s darkness is because the Sun has just begun to rise above the horizon at this very high latitude location (84 degrees). The circular feature is likely a buried ancient crater, with the streaks indicating the prevailing wind direction blowing both sand and frost about.

On August 9, 2019 I provided an update on this monitoring, when new images of this same location were downloaded from MRO in April and June. MRO has now taken a new image of Buzzell, on October 2, 2019. Below the fold are all these images so that you can see the sublimation and disappearance of that dry ice layer over time.

Buzzel dunes, April 4, 2019
Click for full image.

Buzzell dunes, June 4, 2019
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Buzzell dunes, October 2, 2019
Click for full image.

When the first image above was taken in March the Sun was only 5 degrees above the horizon. For the October image below the Sun was 31 degrees above the horizon and was likely above that horizon for all or most of the day. For the Martian north pole, spring had ended and summer had arrived.

Looking at the October image it surely appears to my eye that this onset of summer and its long days has completed the disappearance of that carbon dioxide layer, leaving these dunes completely exposed. The black spots seen in the middle two images to the right and indicative of cracks in that dry ice layer where it has begun to sublimate, splattering dark dust from below across its surface, are gone in October. Instead, we see what appears to be the relatively hard crusty surface of the dunes themselves, as well as the rim of that ancient crater. That crater by the way appears to be a pedestal crater, its floor more resistant to erosion than the surrounding dunes, so that it now sits above them.

I emailed Dr. Hansen to see if my conclusions were correct. Though she said that “all the seasonal ice should be gone by now,” she also noted that she has not yet had time to analyze the image, so this is not yet confirmed.

The research by Hansen and others of these seasonal processes has also found that this sublimation of the dry ice layer also causes annual changes to the dunes. Unfortunately, she also explained to me that she has not yet been able to analyze this most recent image to see if Buzzell had been reshaped in any way due to this spring’s activity.

Meanwhile, the monitoring of avalanches on the nearby edge of the polar ice cap continues. Only a few miles to the north and west of Buzzell are two areas where avalanches have been repeatedly seen coming down from that polar cliff edge, as they happen. In the most recent release of new MRO images are two new images of those cliffs, here and here.

In comparing these new images with previous ones, it appears to my uneducated eye that the avalanche season has ended. While the earlier image of the first example above clearly showed avalanches, as they were occurring with the puffs of clouds at their base, the new image does not.

Avalanches might still be on-going, but it will take some real scientific analysis to determine their changing activity from the spring to the summer months.

Genesis cover

On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.

 
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.


The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
 

"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News

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